WorldClockTools.

Timezone reference

Timezone reference hub.

Start with the most useful IANA zones, abbreviation references, and conversion pairs instead of guessing which timezone page to open first.

Zone references, abbreviations, and conversion pairs refresh on the timezone data update window so the hub stays aligned with the current route catalog.

Offset index

UTC offset strip

UTC−12 · 0 · +14
PDTEDTBSTCESTISTSGTJSTAEST

Each pill links to the zone detail page. Offsets are laid out left-to-right from UTC−12 through UTC+14.

IANA catalog

Popular IANA zones

America/Los_Angeles

PDTUTC-07:00

America/New_York

EDTUTC-04:00

Europe/London

BSTUTC+01:00

Europe/Paris

CESTUTC+02:00

Asia/Kolkata

ISTUTC+05:30

Asia/Singapore

SGTUTC+08:00

Asia/Tokyo

JSTUTC+09:00

Australia/Sydney

AESTUTC+10:00

Browse by region

IANA zones by continent

Each continent rail goes deeper than the popular grid above. Open a zone to see its UTC offset, abbreviation, daylight-saving rules, and the major cities that observe it.

How IANA zones are named

Reading a time-zone ID before you pick one

This hub is a directory of IANA time zones. Knowing how the IDs are built — and how they differ from abbreviations — makes the catalog below far quicker to navigate. For the live multi-city clock, see the world clock; to convert a specific time, use the converter.

How an IANA zone ID is structured

IANA zone IDs follow an Area/Location pattern: a broad area (a continent or ocean such as America, Europe, Asia, Pacific) followed by a representative location, usually the largest city — America/New_York, Asia/Kolkata. Underscores replace spaces. The location is a label for a set of rules, not a claim that only that city uses the zone.

A zone is a rule set, not a city

Each IANA zone represents a region that has shared the same clock — the same offsets and the same daylight-saving transition dates — since 1970. Many cities map to one zone: America/Chicago covers most of the US central band. When two places diverge in their rules, IANA splits them into separate zones.

Zone ID versus abbreviation

An abbreviation such as EST or IST is a short human label and is ambiguous — IST means India, Irish, and Israel Standard Time depending on context, and abbreviations are not standardized. An IANA zone ID is unique and machine-resolvable. Use abbreviations in conversation; use zone IDs whenever the result has to be correct.

The tzdata release cycle

The IANA time-zone database (tzdata) is updated whenever a government changes its offset or daylight-saving policy — typically several releases a year, each tagged like 2025a, 2025b. Operating systems, browsers, and this site pick up those changes when they update their bundled tzdata. That release cycle is why a named zone stays correct while a hard-coded offset eventually goes stale.

Why there are 340-plus zones

There are only about 38 distinct UTC offsets in use, but the tz database defines more than 340 named zones. The extra granularity exists because zones encode history: two regions at the same offset today may have changed their DST rules on different dates in the past, so each needs its own entry to keep historical timestamps accurate.

Links, aliases, and canonical names

tzdata also contains links — aliases that point an old or alternate name at a canonical zone (for example Asia/Calcutta links to Asia/Kolkata). This hub lists the canonical names. If you arrive with a legacy ID, resolve it to its canonical zone before storing or comparing it.
The IANA tz database is the canonical source for every zone ID, offset, and daylight-saving rule listed on this hub. Reference zones by their canonical IANA ID — abbreviations are ambiguous and bare offsets lose their rules.

Browse by offset

IANA zones by UTC offset band

Grouped along the offset axis rather than by continent — useful when you are reasoning about overlap windows and which regions share working hours. Offsets shown are representative standard values; a zone's live offset can differ during daylight saving.

UTC+00:00 to UTC+03:00

Western Europe, Africa, and the Middle East

UTC+05:00 to UTC+08:00

South, Southeast, and East Asia

UTC+09:00 to UTC+13:00

Japan, Korea, Australia, and the Pacific

By population served

The most-populous IANA zones

A handful of zones serve a large share of the world's population — China runs on a single zone, and India's UTC+05:30 covers well over a billion people. These are the zones most timestamps and meetings touch.

Asia/Shanghai

CSTUTC+08:00

Asia/Kolkata

ISTUTC+05:30

Asia/Jakarta

WIBUTC+07:00

America/Sao_Paulo

BRTUTC-03:00

America/New_York

EDTUTC-04:00

Asia/Tokyo

JSTUTC+09:00

Europe/Moscow

MSKUTC+03:00

Asia/Dhaka

BSTUTC+06:00

Short labels

Popular abbreviations

AEST

Open the abbreviation reference page.

CET

Open the abbreviation reference page.

EST

Open the abbreviation reference page.

GMT

Open the abbreviation reference page.

IST

Open the abbreviation reference page.

JST

Open the abbreviation reference page.

PST

Open the abbreviation reference page.

UTC

Open the abbreviation reference page.

Converter pairs

Popular conversion pairs

EST→PST

Open the practical conversion table and city context.

EST→CST

Open the practical conversion table and city context.

EST→MST

Open the practical conversion table and city context.

EST→GMT

Open the practical conversion table and city context.

EST→UTC

Open the practical conversion table and city context.

EST→IST

Open the practical conversion table and city context.

EST→CET

Open the practical conversion table and city context.

EST→CEST

Open the practical conversion table and city context.

EST→JST

Open the practical conversion table and city context.

EST→AEST

Open the practical conversion table and city context.

EST→AEDT

Open the practical conversion table and city context.

EST→BST

Open the practical conversion table and city context.

Related planning pages

Timezone questions usually spill into city clocks, compare pages, or broader scheduling tools once the reference is clear.

Timezone converter

Move straight into the main conversion workflow.

World clock

Open the live city-clock surface after finding the timezone family you need.

Browse city pages

Go from timezone reference into specific city pages with live contextual signals.

Common timezone questions

What does UTC actually stand for, and why do we use it?
UTC is Coordinated Universal Time — it's the world's reference clock, defined by atomic clocks rather than the sun's position. Software, finance, aviation, and the internet itself all use UTC because it never shifts for daylight saving and stays the same everywhere on Earth. Your local time is just UTC plus or minus the offset your country uses.
What's the difference between a time-zone abbreviation and an IANA zone?
An abbreviation like EST or IST is a label — it's quick to say but ambiguous (IST means India Standard Time, Irish Standard Time, and Israel Standard Time depending on the country). An IANA zone like America/New_York or Asia/Kolkata is unique and encodes the full DST history. Use abbreviations for human conversation; use IANA zones whenever the answer has to be reliable.
How do I know which time zone a country uses?
Open the country page on this site — it lists every IANA zone the country observes (some, like the US and Russia, span multiple zones). Each zone page shows the abbreviation, the current UTC offset, and whether the zone observes daylight saving. The IANA tz database is the authoritative source under the hood.
How is an IANA zone ID structured?
IANA zone IDs follow an Area/Location pattern. The area is a continent or ocean — America, Europe, Asia, Africa, Australia, Pacific — and the location is usually the largest representative city, with underscores standing in for spaces. America/New_York and Asia/Kolkata are typical examples. The location names a rule set, not a single city; many places can share one zone.
How many IANA time zones are there?
The tz database defines more than 340 named zones. That is far more than the roughly 38 distinct UTC offsets currently in use, because zones also encode history: two regions at the same offset today may have changed their daylight-saving rules on different dates, so each needs its own entry to keep past timestamps correct.
How often is the IANA tz database updated?
The tz database is released whenever a government changes its offset or daylight-saving policy — usually several times a year, with versions tagged like 2025a and 2025b. Operating systems, browsers, and websites adopt the changes when they refresh their bundled copy of the data, which is why a named zone stays accurate while a hard-coded offset goes stale.
What is a tzdata link or alias?
The tz database includes link entries — aliases that point a deprecated or alternate name at a canonical zone. Asia/Calcutta, for instance, is a link to Asia/Kolkata. This hub lists canonical names; if you encounter a legacy ID, resolve it to its canonical zone before storing or comparing timestamps.
Should I store an offset or an IANA zone?
Store the IANA zone. An offset is correct only for one instant, while a zone carries the complete rule set, so software can compute the right offset for any past or future moment. Keep a UTC timestamp plus the IANA zone, and never persist a bare offset for anything that has to survive a daylight-saving transition.